In CABG procedures, occlusive disease in the coronary arteries is routinely bypassed with segments of saphenous vein removed from the leg. It is advantageous to place the saphenous vein used as the bypass conduit in the non-reversed orientation. For the saphenous vein to be used in the nonreversed orientation, the valves of the vein must be rendered incompetent. Even if the saphenous vein is used in the reversed orientation, the valves of the vein must be rendered incompetent, since competent valve leaflets can be a site for future clot formation behind the leaflet, which can compromise the viability of the graft.
In in situ bypass procedures, occlusive disease in the arterial system of the leg is bypassed with a segment of adjacent saphenous vein left undissected from the surrounding tissue. For blood to flow in its new direction, the valves in the saphenous vein segment must be obliterated. In this procedure, it is often desirable to view the valve-cutting process directly using a fiber optic scope inserted into the vein.
In both the CABG and the in situ procedures, an infusion of physiologic solution into the vein is useful to identify the valve by clearing the field of view and temporarily closing the valves.
Previous efforts to disrupt the valves within a vein have led to a number of devices and techniques.
One form of valvulotome, called a Mills valvulotome, consists of a long, thin shaft with a short, narrow blade at its distal end. The blade is approximately perpendicular to the longitudinal axis of the shaft. The end of the blade remote from the shaft has a small spherical tip. The blade has a cutting edge along substantially all of its proximal edge, while the distal edge is dull.
A significant shortcoming of the L-shaped design of the Mills valvulotome is the propensity for the blade to snag on side branches of the saphenous vein. This tendency is both cumbersome for the surgeon and also can compromise the integrity of the vein graft. The blade of the Mills valvulotome is small enough to enter side branches easily and, once engaged within the branch, can cut the wall of the vein.
Another type of valvulotome design consists of a wire with a large bullet-shaped tip and round guide pulled by a catheter. The cutting element is located at the proximal end of the bullet tip. Valvulotomes of this design include the LeMaitre, Leather, Hall and Insitucat styles. This design is less prone to catching in side branches but has the disadvantages of being bulky, incompatible with angioscopy for visualization of the cutting-process, and is effective only over a narrow range of vein diameters. Also, the Leather, Hall and Insitucat designs require proper rotational orientation to align properly with the valve cusps, a requirement that is difficult to achieve, given their incompatibility with fiber optic viewing. Moreover, devices of this design tend to tear the valve instead of cut it because the cutting force is simultaneously applied to a relatively large area of the valve.
In another valvulotome design, the valve is cut by a plurality of blunt fingers extending from the end of a catheter. The cutter fingers are shielded except when exposed by the user to engage the valve. A fiber optic viewer extends up the center bore of the catheter to directly observe the cutting process. In this design, the fiber optics are an integral pan of the valvulotome. This design, with its many moving parts, has the disadvantage of being difficult to manufacture. Moreover, the fingers' bluntness, as well as their plurality, tend to rip the valve in a random manner, leaving the vein wall in an unpredictable condition.